The invention relates to a separation column for analyzing gases.
Separation columns are for example used for analyzing natural gas and for determining the calorific value of the natural gas. A separation column which is configured as a capillary is already known. The capillary is filled with a carrier material in the form of spheres which are made from carbon and have a diameter of 150 xcexcm to 200 xcexcm. The separation column has a diameter of a few millimeters and a length of several meters. This separation column can be used to separate the inert gases contained in the natural gas from the fractions which have a calorific value, so that it is possible to determine the calorific value of the gas which is to be analyzed. Five minutes are required to carry out the measurement, and during this period approximately 15 ml of carrier gas have to be passed through the separation column per second.
Separation columns are in increasing demand in microtechnology in order to carry out a rapid analysis of gases. The separation column described above is much too large to be used for this application. In addition, too much time is required for the analysis of a gas. Moreover, for devices with dimensions in the millimeter range, which require a suitable separation column, it is not possible to provide relatively large quantities of carrier gas for every analysis.
It is accordingly an object of the invention to provide a separation column which overcomes the above-mentioned disadvantages of the heretofore-known separation columns of this general type and which has dimensions such that the separation column can be integrated in any device used in microtechnology while also being able to individually separate natural gas into all its constituents, so that its calorific value can be determined therefrom.
With the foregoing and other objects in view there is provided, in accordance with the invention, a separation column for analyzing gases, including:
a capillary having an inner diameter;
spheres having substantially identical diameters, the spheres being disposed as a separation material in the capillary; and
each of the substantially identical diameters of the spheres being matched to the inner diameter of the capillary or being marginally smaller than the inner diameter of the capillary.
According to another feature of the invention, the spheres are made of carbon or Carbosphere carbon.
According to yet another feature of the invention, the inner diameter of the capillary is substantially 200 xcexcm, and the substantially identical diameters of the spheres are between 150 xcexcm and 200 xcexcm.
According to another feature of the invention, the spheres are disposed inside the capillary such that all of the center points of the spheres are provided along a straight line.
According to a further feature of the invention, an inert powder is provided between the spheres at least in given regions inside the capillary.
According to another feature of the invention, the inert powder is made from carbon, Buckminister Fullerene C60 or Carbosphere carbon.
According to another feature of the invention, a respective gas-permeable closure is provided at each of the two ends of the capillary.
According to yet another feature of the invention, the inner diameters of two further capillaries are slightly smaller than the substantially identical diameters of the spheres, and the outer diameters of the two further capillaries are matched to the inner diameter of the capillary. The two further capillaries each have a respective first end inserted in a respective one of the two ends of the capillary, the two further capillaries being connected to the capillary in a gastight and permanent manner such that the two further capillaries form gas-permeable closures at the two ends of the capillary.
According to a further feature of the invention, a support element includes a plate and a cover, the plate and the cover being made from glass or silicon. The plate has a surface and has a channel formed in the surface, the channel having relatively wider sections for receiving the spheres and the channel having relatively narrower sections in front of and behind each of the relatively wider sections. The cover closes off the channel in a gastight manner with respect to an outside environment for providing the capillary, the channel having an end serving as an inlet opening for a carrier gas and a sample gas.
According to another feature of the invention, a support element includes a plate and a cover, the plate and the cover being made from glass or silicon. The plate and the cover have respective surfaces facing one another and have a channel formed partially in each of the surfaces, the channel having relatively wider sections for receiving the spheres and the channel having relatively narrower sections in front of and behind each of the relatively wider sections. The cover closes off the channel in a gastight manner with respect to an outside environment for providing the capillary. One end of the channel serves as an inlet opening for a carrier gas and a sample gas or test gas.
The separation column according to the invention is configured as a thin capillary. Its length is approximately 30 mm and its internal diameter is 150 xcexcm to 200 xcexcm. It is filled with a separation material made from carbon. The carbon is in the form of spheres with a diameter of between 150 xcexcm and 180 xcexcm. If the diameter of the spheres is selected to be greater than this, the distance between the internal diameter of the capillary and the spheres becomes too small. The separation column then becomes very sensitive to bending stresses and may break. To enable natural gas to be sufficiently separated into all its constituents, the spheres made from carbon have to be provided in a very specific form within the capillary. Optimum operation of the separation column according to the invention is achieved if all the spheres are provided in a row one behind the other, so that there are no spheres positioned next to one another, but rather each sphere is provided individually along the axis of the capillary. The result of this structure is that the natural gas is separated into the constituents methane, carbon dioxide, nitrogen, helium, hydrogen sulphide and arsenic compounds, as well as higher molecular hydrocarbons, such as ethane, propane, isobutane, butane and hexane, provided that all these constituents are contained in the natural gas.
To ensure that the spheres are held permanently in the capillary, a gas-permeable closure is provided at each of the two ends of the capillary. Preferably, each of the closures is formed by a capillary, the internal diameter of which is smaller than the diameter of the spheres and one end of which is fitted into the end of the separation column and is connected in a gastight manner thereto. An adhesive in the form of epoxy resin is preferably used to connect the closures to the separation column. Since the two closures at the ends of the separation columns are configured as capillaries, it is possible for the gas which is to be analyzed and also the carrier gas to be introduced into the separation column without problems. Moreover, the components or eluents into which the gas which is to be analyzed is separated in the separation column, and also the carrier gas, can escape without difficulty from the second end of the separation column.
The maximum separation capacity of the separation column, i.e. its highest plate number, is achieved at a flow of approximately 5 xcexcl/sec if hydrogen is used as carrier gas. Natural gas is separated into the constituents CO2, methane and air in less than 16 sec if the temperature is increased from 0xc2x0 C. to approximately 50xc2x0 C. in this time period.
The flow rate range of high plate number can be widened downward if an inert powder in the form of Buckminister Fullerene C60 is positioned between the individual spheres of carbon. Instead of this powder, it is also possible to use a carbon powder, which is also used to produce the spheres described above. A powder made from Carbosphere carbon is also suitable for this purpose.
An addition of such a powder reduces the flow through the separation column. However, if the flow rate along the active surfaces of the separation column which is filled with spheres and an inert powder is to be maintained at the same level in order to obtain the maximum number of plates, the overall flow through the capillary is to be reduced.
Because of the inert powder which fills the spaces between the carbon spheres, there are numerous different ways for the gases to flow through the separation column past the spheres. Because of these measures, the number of plates is independent within wide ranges, over virtually an order of magnitude, of the overall flow through the separation column or the admission pressure of the carrier gas. It is therefore possible, for the separation column according to the invention, for the flow to be set according to other, independent criteria while maintaining the number of plates. One such criterion may, for example, be a defined flow which requires an additional separation column or another component connected upstream of the separation column according to the invention.
As mentioned above, the separation column according to the invention is provided for use in microsystems technology. Therefore, the separation column may also be formed directly in a support element, through the use of which a large number of Microsystems technology components can be combined to form a single unit. Support elements of this type are provided with a plate and a cover made from glass or silicon. The cover delimits the surface of the plate in a gastight manner with respect to the outside. For the separation column, a channel is formed in the surface of the plate. The channel is provided with widened sections, the diameters of which are slightly larger than the diameters of the carbon spheres. Then, a sphere of carbon is provided in each widened section of the channel. In front of and behind each widened section, the channel is narrowed to a diameter which is no greater than the inlet opening of the channel. The result is that the spheres provided in the widened sections are held in place. In the region of the widened sections, the diameter of the channel is no greater than the internal diameter of the capillary described above. The channel is also of the same length as the capillary. After the spheres have been provided in the channel, the cover is connected to the surface of the plate in such a way that the channel is closed off in a gastight manner.
It is also possible for the channel to be formed partially in the cover and partially in the surface of the plate. In this case, at the locations at which in each case one sphere is to be provided in the channel, the cover is likewise provided with a deeper recess, the channel in this case too being narrowed in front of and behind each widened section. Therefore, in this way too it is possible to form a separation column as described above. Forming the separation column partially in the cover and partially in the plate has the advantage that the recesses in either the plate or the cover do not have to be as deep as if the separation column is formed only in the surface of the plate. Consequently, the cover and the plate can be of thinner configuration. The first end of the separation column is open so that a gas which is to be analyzed and carrier gas can be introduced into the channel. The second end of the channel may be connected to a detector, which may likewise be provided in a recess in the plate.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a separation column for the analysis of gases, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.